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.\"     From: @(#)inet.3	8.1 (Berkeley) 6/4/93
.\"	$Id: inet.3,v 1.1.1.1 2006/05/30 06:12:06 hhzhou Exp $
.\"
.Dd June 17, 1996
.Dt INET 3
.Os BSD 4.2
.Sh NAME
.Nm inet_aton ,
.Nm inet_addr ,
.Nm inet_network ,
.Nm inet_ntoa ,
.Nm inet_makeaddr ,
.Nm inet_lnaof ,
.Nm inet_netof
.Nd Internet address manipulation routines
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Fd #include <netinet/in.h>
.Fd #include <arpa/inet.h>
.Ft int 
.Fn inet_aton "const char *cp" "struct in_addr *pin"
.Ft unsigned long 
.Fn inet_addr "const char *cp"
.Ft unsigned long 
.Fn inet_network "const char *cp"
.Ft char *
.Fn inet_ntoa "struct in_addr in"
.Ft struct in_addr 
.Fn inet_makeaddr "unsigned long net" "unsigned long lna"
.Ft unsigned long 
.Fn inet_lnaof "struct in_addr in"
.Ft unsigned long 
.Fn inet_netof "struct in_addr in"
.Sh DESCRIPTION
The routines
.Fn inet_aton ,
.Fn inet_addr
and
.Fn inet_network
interpret character strings representing
numbers expressed in the Internet standard
.Ql \&.
notation.
The
.Fn inet_aton
routine interprets the specified character string as an Internet address,
placing the address into the structure provided.
It returns 1 if the string was successfully interpreted,
or 0 if the string is invalid.
The
.Fn inet_addr
and
.Fn inet_network
functions return numbers suitable for use
as Internet addresses and Internet network
numbers, respectively.
The routine
.Fn inet_ntoa
takes an Internet address and returns an
.Tn ASCII
string representing the address in
.Ql \&.
notation.  The routine
.Fn inet_makeaddr
takes an Internet network number and a local
network address and constructs an Internet address
from it.  The routines
.Fn inet_netof
and
.Fn inet_lnaof
break apart Internet host addresses, returning
the network number and local network address part,
respectively.
.Pp
All Internet addresses are returned in network
order (bytes ordered from left to right).
All network numbers and local address parts are
returned as machine format integer values.
.Sh INTERNET ADDRESSES
Values specified using the
.Ql \&.
notation take one
of the following forms:
.Bd -literal -offset indent
a.b.c.d
a.b.c
a.b
a
.Ed
.Pp
When four parts are specified, each is interpreted
as a byte of data and assigned, from left to right,
to the four bytes of an Internet address.  Note
that when an Internet address is viewed as a 32-bit
integer quantity on the
.Tn VAX
the bytes referred to
above appear as
.Dq Li d.c.b.a .
That is,
.Tn VAX
bytes are
ordered from right to left.
.Pp
When a three part address is specified, the last
part is interpreted as a 16-bit quantity and placed
in the right-most two bytes of the network address.
This makes the three part address format convenient
for specifying Class B network addresses as
.Dq Li 128.net.host .
.Pp
When a two part address is supplied, the last part
is interpreted as a 24-bit quantity and placed in
the right most three bytes of the network address.
This makes the two part address format convenient
for specifying Class A network addresses as
.Dq Li net.host .
.Pp
When only one part is given, the value is stored
directly in the network address without any byte
rearrangement.
.Pp
All numbers supplied as
.Dq parts
in a
.Ql  \&.
notation
may be decimal, octal, or hexadecimal, as specified
in the C language (i.e., a leading 0x or 0X implies
hexadecimal; otherwise, a leading 0 implies octal;
otherwise, the number is interpreted as decimal).
.Pp
The
.Fn inet_aton
and
.Fn inet_ntoa
functions are semi-deprecated in favor of the
.Xr addr2ascii 3
family.  However, since those functions are not yet widely implemented,
portable programs cannot rely on their presence and will continue
to use the
.Xr inet 3
functions for some time.
.Sh DIAGNOSTICS
The constant
.Dv INADDR_NONE
is returned by
.Fn inet_addr
and
.Fn inet_network
for malformed requests.
.Sh SEE ALSO
.Xr addr2ascii 3 ,
.Xr gethostbyname 3 ,
.Xr getnetent 3 ,
.Xr hosts 5 ,
.Xr networks 5
.Sh HISTORY
These
functions appeared in 
.Bx 4.2 .
.Sh BUGS
The value
.Dv INADDR_NONE
(0xffffffff) is a valid broadcast address, but
.Fn inet_addr
cannot return that value without indicating failure.
The newer
.Fn inet_aton
function does not share this problem.
The problem of host byte ordering versus network byte ordering is
confusing.
The string returned by
.Fn inet_ntoa
resides in a static memory area.
.Pp
Inet_addr should return a
.Fa struct in_addr .
